Donald,
At this point, I'm most interested in strengthening the external rotators so that they can maintain the fully rotated position on their own. I want people to be able to externally rotate actively, not passively like in that stretch (and doing PNF in that position only strengthens the internal rotators, something most people don't need more of).

The teacup stuff is nice. I do other shoulder work and find that I can still maintain the teacup capability just fine, so I personally don't have much time for it.